1. Field of the Invention
The present invention relates to a thin film magnetic head having a function of dissipating heat generated in a magnetoresistive effect film to outside, a method of manufacturing the same, and a magnetic disk drive comprising the thin film magnetic head.
2. Description of the Related Art
In recent years, an improvement in performance of thin film magnetic heads has been sought in accordance with an improvement in areal density of hard disk drives. As the thin film magnetic heads, composite thin film magnetic heads (hereinafter simply referred to as “thin film magnetic heads”) are widely used. The composite thin film magnetic head comprises a laminate including a reproducing head portion having a magnetoresistive device (hereinafter referred to “MR device”), which is a kind of magnetic transducer, and a recording head portion having an inductive magnetic transducer.
As a typical MR device, a GMR device using a magnetic film (GMR film) exhibiting a giant magnetoresistive effect (hereinafter referred to as “GMR effect”) is cited. In particular, a GMR device using a spin-valve type GMR film has been in the mainstream. The spin-valve type GMR film has a relatively simple structure, thereby is suitable for mass production, and exhibits a large change in magnetoresistance in spite of an extremely weak magnetic field. Such a GMR device has the following structure.
FIG. 18 shows a schematic sectional view of a structure of a conventional reproducing head portion including the GMR film. A reproducing head portion 110A has the following structure. On a base substrate (not shown) made of, for example, AlTiC (Al2O3—TiC) or the like, a bottom shield layer 101 made of a magnetic material is laminated with an insulating layer (not shown) made of, for example, aluminum oxide (Al2O3) or the like in between. On the bottom shield layer 101, a bottom gap layer 102 made of, for example, an insulating material such as aluminum oxide or the like is formed, and on the bottom gap layer 102, a GMR film 120 and an insulating layer 103 are formed so as to be adjacent to each other. On the GMR film 120 and the insulating layer 103, a top gap layer 105 is laminated. A bottom surface and a top surface of the GMR film 120 are in contact with the bottom gap layer 102 and the top gap layer 105, respectively. On one side end surface of the GMR film 120, a recording-medium-facing surface 119 facing a magnetic recording medium 11 is formed, and an end surface of the GMR film 120 on a side opposite to the recording-medium-facing surface 119 is in contact with the insulating layer 103. As in the case of the GMR film 120, a bottom surface and a top surface of the insulating layer 103 are in contact with the bottom gap layer 102 and the top gap layer 105, respectively. Further, on the top gap layer 105, a top shield layer 106 made of a magnetic material is laminated.
On the reproducing head portion 110A, a recording head portion (not shown) is laminated, and the combination of the reproducing head portion 110A and the recording head portion constitutes a thin film magnetic head 110.
In general, a length from the recording-medium-facing surface 119 to an end surface on a side opposite to the recording-medium-facing surface 119 in the MR device is called an MR height (or an MR device height). On the other hand, a length of the MR device in a direction perpendicular to a paper surface of FIG. 18 is a portion corresponding to a track width of a recording medium (hereinafter referred to as “MR device width”). Recently, in order to cope with a remarkable increase in recording density, the MR device width is becoming increasingly smaller. Accordingly, the MR height is also becoming increasingly smaller.
A problem resulting from heat generated in the MR device occurs due to a downsizing of the MR device. The problem is that due to the heat generated in the MR device, electromigration (a phenomenon in which a void is locally formed when metal atoms move in a conductor) or interlayer diffusion is induced, and as a result, it is difficult to sufficiently extend the lifetime of the MR device. The heat generated in the GMR device 120 is transferred to the top shield layer 106 and the bottom shield layer 101 through the top gap layer 105 and the bottom gap layer 102 to be dissipated. However, when the MR height and the MR device width become smaller, a heat dissipation area, that is, the whole surface area of the GMR film 120 is greatly reduced as a inevitable consequence, so sufficient heat dissipation can not be achieved. It can be considered that when the MR device becomes still thinner (smaller) in future, the temperature of the MR device will excessively rise to, for example, higher than 50° C., and as a result, electrical resistance of the thin film magnetic head will increase. In extreme cases, element diffusion may occur in the MR device, thereby characteristics of thin film magnetic head may be pronouncedly degraded. Further, it can be considered that even if the temperature of the MR film does not rise to as high as internal element diffusion occurs, a degradation in the characteristics resulting from the heat generated in the GMR film 120 such as a reduction in output during reproducing magnetically recorded information resulting from increased electrical resistance may occur.
As an MR device with improved heat dissipation, for example, a thin film magnetic head disclosed in Japanese Unexamined Patent Application Publication No. Hei 6-223331 is cited. In the thin film magnetic head disclosed in the publication, as an insulating layer of an MR device, a material with good insulation and good thermal conductivity such as a silicon film, a diamond-like carbon or the like is used so as to carry out heat dissipation of the MR device. Moreover, in a thin film magnetic head and a magnetic disk drive disclosed in Japanese Unexamined Patent Application Publication No. 10-222816, as not only an insulating layer of an MR device, but also a protective film of a magnetic head slider or a disk surface, a non-magnetic insulating film with a high heat dissipation ratio such as a hydrogen-containing amorphous carbon film, silicon-containing amorphous carbon, amorphous aluminum nitride or the like is used. Thereby, the occurrence of a phenomenon called thermal asperity (TA) resulting from heat caused by friction between the magnetic head slider and the magnetic disk, electromigration or the like can be prevented, so the characteristics of read output can be improved. However, even if the thermal conductivity of a component material around the MR device is higher, the heat dissipation area of the component around the MR device is relatively reduced resulting from a downsizing of the MR device, so heat dissipation capacity is limited.
The applicant of the present invention has been proposed a thin film magnetic head disclosed in Japanese Unexamined Patent Application Publication No. 2000-353308, which can overcome the above-described problem. An enlarged sectional view of a specific example of the thin film magnetic head disclosed in the publication is shown in FIG. 19. In the thin film magnetic head, a reproducing head portion 210A comprises a heat dissipation layer 104 in contact with a laminated surface of the GMR film 120, and heat generated in the GMR film 120 is dissipated to outside through the heat dissipation layer 104.
However, even in the case of the thin film magnetic head disclosed in the above publication, when a demand for a thinner MR device (a downsizing of the MR film in a thickness direction) grows in accordance with an even higher recording density in future, the heat dissipation layer 104 cannot have a sufficient thickness, and as a result, it can be expected that it will be more difficult to secure sufficient heat dissipation.